9. Neuromuscular System

Question 1

The role of the sympathetic and parasympathetic nervous systems

Answer 1

The sympathetic and parasympathetic nervous systems transmit information from the brain to the parts of the. Odd that need to adjust what they are doing in order to prepare for or recover from exercise

• The sympathetic nervous system fires up the body for exercise and is often referred to as the ‘fight or flight response’
• the parasympathetic nervous system slows everything down and slows down many high-energy functions. It is often explained by the phrase ‘rest and relax’

Question 2

The characteristics and functions of the three muscle fibre types (type 1, type IIa, type IIx)

Answer 2

Type 1-
-are slow twitch fibres. These are better adapted to low-intensity, long duration exercise. They produce their energy aerobically and have specific characteristics that allow them to use oxygen more effectively

Type II-
-are fast twitch fibres and can generate a greater force of contraction. They produce most of their energy anaerobically. Type IIa fibres (fast oxidative glycolytic) are more resistant to fatigue and are used for events such as the 1500m in athletics, where a longer burst of energy in needed

Type IIx (fast glycolytic)
-fibres fatigue quickly and are used for highly explosive events such as the 100m in athletics or power lifting

Question 3

The characteristics and functions of the three fibre types

Answer 3

-Structural characteristic: motor neurone size
Type 1: small
Type IIa: large
Type IIx: large

-Mitochondrial density
High
Medium
Low

-myoglobin content
High
Medium
Low

-capillary density
High
Medium
Low

-PC and glycogen store
Low
High
High

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-Function: contraction speed (milliseconds)
Type 1: slow (110)
Type IIa: fast (50)
Type IIx: fast (50)

-motor neurone conduction capacity
Slow
Fast
Fast

-force produced
Low
High
High

-fatiguability
Low
Medium
High

-aerobic capacity
Very high
Medium
Low

-anaerobic capacity
Low
High
Very high

-Myosin ATPase/glycolytic enzyme activity
Low
High
Very high

Question 4

The recruitment of muscle fibres using motor units to provide maximal contractions (motor units, spatial summation,wave summation, titanic contraction, all or none law)

Answer 4

• muscle fibres are grouped into motor units
• a motor u it comprises a motor neurone and its muscle fibres. Each muscle is made up of many motor u it’s and these vary in size. A small muscle that is used for fine motor control has small motor units; a large muscle used for gross motor control has large motor units.

-motor units contain the face type of muscle fibre, so they are either slow twitch or fast twitch motor units. To achieve MAXIMAL CONTRACTION, we need to use large motor units containing fast-twitch fibres and recruit lots of these motor units.

You also have to ensure that the following takes place:
•the sequence of impulses had to be sufficient intensity to stimulate all of the muscle fibres in a motor unit in order for them to contract, I.e the
all or none law is full filled
•wave summation-where there is a repeated nerve impulse with no time to relax, so a smooth, sustained contraction occurs rather than twitches
•tetanic contraction- a sustained, powerful muscle contraction caused by a series of fast repeating stimuli
•spatial summation- where the strength of a contraction changes by altering the number and size of the muscle motor units used

Question 5

Role of proprioreceptors in PNF (muscle spindles, golgi tendon organs)

Answer 5

• Muscle spindles are proprioceptors that send exciting signals to the CNS about how far and how fast a muscle is being stretched. The CNS then sends impulses to the muscle to cause it to contract and produce the stretch reflex
• Golgi tendon organs detect levels of tension in a muscle. When the muscle is contracted isometrically in PNF they sense the increase in muscle tension and send inhibitory signals to the brain, which allows the antagonist muscle to relax and lengthen. This is know as autogenic inhibition.

-autogenic inhibition is where there is a sudden relaxation of the muscle in response to high tension

Question 6

PNF in practice

Answer 6

The individual performers a passive stretch of the hamstrings until tension is felt. This stretch is then detected by the muscle spindles. If the muscle is being stretched too far then a stretch reflex occurs

The individual them isometrically contracts the muscle for at least 10 seconds by pushing their leg against their partner, who supplies just enough resistance to hold the individuals leg in place. Golgi tendon organs are sensitive to tension developed in the muscles and during an isometric contraction they are activated and the inhibitory signals they send override the excitatory signals from the muscle spindles, therefore delaying the stretch reflex

As the leg is passively stretched again, the Golgi tendon organs are responsible for the antagonist muscle replacing which means the leg stretches further. This process can be repeated until no more gains are possible